I have a question about the flight engineer positions on UPS' DC-8s and 727s and Fedex 727s. In a previous thread about Fedex 737s, someone mentioned that the Fedex flight engineers are not professional flight engineers but pilots who will eventually be promoted to first officers. I assume that flight engineers for UPS are in the same position.

Do the flight engineers for these two airlines take turns with the first officers in actually taking off, flying and landing the aircraft? If not how do they keep their flying skills current besides time in the simulator?

Many F/Es with UPS and FedEx are not pilots. I do not know how their number compares to the F/Es that are actually pilots and waiting for an opening as first officer, by seniority as their company rules are.
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Maintaining pilot proficiency when you are a F/E is rather difficult. The F/E is not legally permitted to occupy a pilot seat for takeoff, cruise or landing, if he is not qualified and current as such. A pilot trading seats with a F/E would have to meet same requirements to occupy the F/E station...
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In the old days, airlines provided simulator practice for pilots who wanted to maintain proficiency, but cost saving measures have all but stopped that liberal attitude.
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I have seen and heard extreme cases of pilots with some airlines, who were F/E for many years having completely lost their proficiency as pilot. For many it was their own fault. They continued to bid by choice a F/E position to bigger - better paying airplanes - rather than bidding a first officer position in more junior airplanes. Some pilots who were F/E for sometimes 10 or 15 years, were basically unable to be retrained to proficiency. They then did continue as F/E until the end of their careers. Regrettable.
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Happy contrails
(s) Skipper

FDXmech is correct, all the engineer's at FedEx are pilots. Some of them are over 60 guys that were former captains or first officers. As an S.O. it's up to you to maintain your currency if you choose. I was on the panel for two years before I upgraded to the right seat and I flew a little bit in a Cessna 152 for fun. Flying is like riding a bike so unless you are out of it for a really long time then it comes back to you pretty quick.

There are F/E's at Fed Ex and UPS who are not pilots, but they have been flying the line for many years as flight engineers. When they joined the airlines they didn't have to have pilot ratings, they just needed the Professional Flight Engineer FAA license, but that is no longer true of course.
Now all F/E's are S/O's, they have to take the F/E written exam to be considered for an interview but they need to have at least Commercial, IFR, Multi, and CFI ratings, and like in every airline there is a minimum number of flight hours a pilot applicant must have. You can't apply today at Fed Ex or UPS if you just want to fly as flight engineer all your life, all young flight engineers are pilots. They fly as S/O and two years after their date of hire they can move to the first officer's seat when there is a vacancy.

Two years ago when American was retirering the last 727's, there were still professional F/E's flying on those, they were over 60 and they had up to 40 years of experience in various aircraft types including the Electra, DC-6, B707, B747 and DC-10.
There was once in Airways an article about flying the IL-86, which requires besides the two pilots a flight engineer and a navigator. The F/E had been flying in the engineer's station all his life in several russian models and the DC-10. If I remember well what I read in the article, that's the rule in Russia contrary to what it is today in the United States. When you start as F/E you do that all your life.